6,732 research outputs found
Conditional entropy of ordinal patterns
In this paper we investigate a quantity called conditional entropy of ordinal
patterns, akin to the permutation entropy. The conditional entropy of ordinal
patterns describes the average diversity of the ordinal patterns succeeding a
given ordinal pattern. We observe that this quantity provides a good estimation
of the Kolmogorov-Sinai entropy in many cases. In particular, the conditional
entropy of ordinal patterns of a finite order coincides with the
Kolmogorov-Sinai entropy for periodic dynamics and for Markov shifts over a
binary alphabet. Finally, the conditional entropy of ordinal patterns is
computationally simple and thus can be well applied to real-world data
Effects of Raman scattering and attenuation in silica fiber-based parametric frequency conversion
Four-wave mixing in the form of Bragg scattering (BS) has been predicted to
enable quantum noise less frequency conversion by analytic quantum approaches.
Using a semi-classical description of quantum noise that accounts for loss and
stimulated and spontaneous Raman scattering, which are not currently described
in existing quantum approaches, we quantify the impacts of these effects on the
conversion efficiency and on the quantum noise properties of BS in terms of an
induced noise figure (NF). We give an approximate closed-form expression for
the BS conversion efficiency that includes loss and stimulated Raman
scattering, and we derive explicit expressions for the Raman-induced NF from
the semi-classical approach used here.Comment: 14 single col pages, 11 figure
Rectification in single molecular dimers with strong polaron effect
We study theoretically the transport properties of a molecular two level
system with large electron-vibron coupling in the Coulomb blockade regime. We
show that when the electron-vibron coupling induces polaron states, the
current-voltage characteristic becomes strongly asymmetric because, in one
current direction, one of the polaron state blocks the current through the
other. This situation occurs when the coupling between the polaron states is
smaller than the coupling to the leads. We discuss the relevance of our
calculation for experiments on C_140 molecules.Comment: 4 pages, 4 figure
Nonlocal Damping of Helimagnets in One-Dimensional Interacting Electron Systems
We investigate the magnetization relaxation of a one-dimensional helimagnetic
system coupled to interacting itinerant electrons. The relaxation is assumed to
result from the emission of plasmons, the elementary excitations of the
one-dimensional interacting electron system, caused by slow changes of the
magnetization profile. This dissipation mechanism leads to a highly nonlocal
form of magnetization damping that is strongly dependent on the
electron-electron interaction. Forward scattering processes lead to a spatially
constant damping kernel, while backscattering processes produce a spatially
oscillating contribution. Due to the nonlocal damping, the thermal fluctuations
become spatially correlated over the entire system. We estimate the
characteristic magnetization relaxation times for magnetic quantum wires and
nuclear helimagnets.Comment: Final version accepted by Physical Review
Coplanar constant mean curvature surfaces
We consider constant mean curvature surfaces of finite topology, properly
embedded in three-space in the sense of Alexandrov. Such surfaces with three
ends and genus zero were constructed and completely classified by the authors
in arXiv:math.DG/0102183. Here we extend the arguments to the case of an
arbitrary number of ends, under the assumption that the asymptotic axes of the
ends lie in a common plane: we construct and classify the entire family of
these genus-zero coplanar constant mean curvature surfaces.Comment: 35 pages, 10 figures; minor revisions including one new figure; to
appear in Comm. Anal. Geo
Triunduloids: Embedded constant mean curvature surfaces with three ends and genus zero
In 1841, Delaunay constructed the embedded surfaces of revolution with
constant mean curvature (CMC); these unduloids have genus zero and are now
known to be the only embedded CMC surfaces with two ends and finite genus.
Here, we construct the complete family of embedded CMC surfaces with three ends
and genus zero; they are classified using their asymptotic necksizes. We work
in a class slightly more general than embedded surfaces, namely immersed
surfaces which bound an immersed three-manifold, as introduced by Alexandrov.Comment: LaTeX, 22 pages, 2 figures (8 ps files); full version of our
announcement math.DG/9903101; final version (minor revisions) to appear in
Crelle's J. reine angew. Mat
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